Now, she is in the custody of the Irish police, along with six other individuals, arrested as part of an investigation into a conspiracy to commit murder, according to officials familiar with the case. The nature of the authorities’ suspicions about Ms. Paulin-Ramirez couldn’t be determined on Friday.

Ms. Paulin-Ramirez’s interest in Islam “came out of left field,” said her mother, Christine Holcomb-Mott, in an interview at her home Friday, wearing a blue sweatsuit with a silver cross around her neck.

Last Easter, Jamie Paulin-Ramirez, a 31-year-old mom with a $30,000-a-year job as a medical assistant, announced to her family that she had converted to Islam. A few months later, she began posting to Facebook forums whose headings included “STOP caLLing MUSLIMS TERRORISTS!”

On Sept. 11, she suddenly left Leadville, Colo., a small town in the Rocky Mountains, for Denver, then for New York, to meet and marry a Muslim man she connected with online, her family says. Ms. Paulin-Ramirez, who is 5-foot-11 and blonde, phoned her mother and stepfather in Leadville, providing them with an address in Waterford, Ireland, they say.

Jamie Paulin-Ramirez, a 31-year-old mom, is in the custody of the Irish police, along with six other individuals, arrested as part of an investigation into a conspiracy to commit murder.